Tens of millions of reproductive age women in the U.S. have uterine leiomyomata, commonly called fibroids; yet, the influence of fibroids in pregnancy and vice versa is poorly understood. We propose to examine the association of fibroids with specific adverse pregnancy outcomes while investigating the natural history of fibroids during and after pregnancy. We will advance current knowledge by: recruiting an ethnically diverse population early in pregnancy; using a standardized research protocol to conduct ultrasound (US) for all participants to reduce fibroid misclassification; refining assessment of pregnancy events and outcomes; and investigating how size and location of fibroids affect risk. Based on procedures in place for "Right from the Start: A Study of Early Pregnancy Health", we propose to build a cohort of 3,300 women from 13 counties in North Carolina. We will include approximately 15% Hispanic, 35% African American, and 45% white women, obtaining an US in the 6-7th wk of gestation and a computer assisted telephone interview (CATI) before 10wks gestation. A second CATI, at 20-22 wks, and documentation of outcome, including medical record review, will be done for all medical participants. We will also randomly select a subcohort of 300 women from among those with fibroids and 100 from those without fibroids on 1st trimester US in return for US at 14-16 weeks, 26-28 wks, and 3 months post-pregnancy. In the subcohort, we will conduct a final CATI 3 months after pregnancy. By doing so, we will answer these primary research questions: 1. Are women with fibroids at higher risk of spontaneous abortion (SAB)? 2. Are women with fibroids at higher risk for a spontaneous preterm birth (PTB)? and these secondary questions: 3. Is fibroid size or submucosal location associated with increased risk of SAB or PTB? 4. Are fibroids beneath the placenta associated with increased risk of PTB? 5. Are fibroids likely to change size during and after pregnancy? Is growth pattern related to age, race, BMI, maternal weight gain, clinical glucose tolerance measures, hypertension, pregnancy outcome, lactation, or post-pregnancy contraceptive choice? If fibroids, or certain fibroids, have an adverse effect on pregnancy, the clinical and public health consequences would be substantial given the high prevalence of fibroids. By prospectively investigating fibroid characteristics and risk, this research has potential to inform care for many women with fibroids who are pregnant or planning pregnancy.